The proposed research includes studies on the development and organization of the vertebrate visual system, with emphasis on the retina. The proposal encompasses the following projects: 1) An ultrastructural study of synaptogenesis in human cones. 2) A study of the photoreceptor-pigment epithelial cell relationship in the mammalian retina. 3). The development of cat cones and the pigment epithelial sheath which contacts cone outer segments. 4) The effect of vitamin A deficiency on ground squirrel cones. A determination of the extent of degeneration that occurs in cones during deficiency and the ability of degenerate cones to regenerate. 5) The renewal of Xenopus photo-receptor outer segments in vitro and the effect of light on this process. 6) A study of synaptic organization of the optic tectum in goldfish, including the normal rectum, after optic nerve degeneration, and after compression of the retinal projection. 7) A study to determine if ground squirrels which show no ERG evidence of rod function do have anatomically normal rods. BIBLIOGRAPHIC REFERENCES: Jacobs, G.H., Fisher, S.K., Anderson, D.H., & Silverman, M.A. 1976. Scotopic and phototopic vision in the California ground squirrel: Physiological and anatomical evidence. J. Comp. Neurol. 165: 473-480. Anderson, D.H. & Fisher, S.K. 1976. The photoreceptors of diurnal squirrels: Outer segment structure, disc shedding, and protein renewal. J. Ultrastruct. Res. 55:119-141.